1. Field of the Invention
The present invention relates to an inkjet printer and a cap unit for maintenance unit of the inkjet printer.
2. Description of the Related Art
In a head of an inkjet printer, a large number of nozzles are formed to eject ink there from so that printing can be carried out on recording paper or various sheet-like recording media (hereinafter also referred to collectively as “paper-like recording medium”). When ink is ejected through the nozzles, ink is supplied thereto. Therefore, the nozzles are always filled with ink.
When such a head is exposed to the atmosphere for a long time without carrying out printing, a solvent component evaporates gradually from the ink in the nozzles so that the ink in the nozzles may increase in concentration or the inside of each nozzle may be dried. In such a state, ink cannot be ejected properly from the nozzles. Thus, the quality of printing is deteriorated.
Therefore, the inkjet printer is provided with a cap, which comes into close contact with the head when the head does not engage in printing, in order to prevent the ink in the nozzles from increasing in concentration or the inside of each nozzle from being dried (for example, see JP-A-2001-301186 and JP-A-2002-301831).
Even though such a cap is provided, passage of a long time may result in evaporation of the solvent component from the ink so that the ink charged into the nozzles may increase in concentration. At a time of starting printing, processing for bringing the cap into close contact with the head while ejecting ink from the head to thereby eliminate high-concentration ink from the head (hereinafter also referred to as “purge processing”) is therefore performed (see the paragraph [0010] in JP-A-2001-301186 and the paragraph [0035] in JP-A-2002-301831).
JP-A-2001-301186 and JP-A-2002-301831 disclose the following purge processing system. In the disclosed purge processing system, a negative pressure is generated in a cap by use of a suction pump so as to generate a difference in pressure between an ink flow channel on the upstream side of the head and the inside of the cap, by which ink is ejected from the head. In the following description, this purge processing system will be referred to as “suction system”.
On the other hand, the present inventor has examined another purge processing system in which the pressure is increased in an ink flow channel on the upstream side of the head by use of a pressure pump so as to generate a different in pressure between the ink flow channel on the upstream side of the head and the inside of the cap, by which ink is ejected from the head. In the following description, this purge processing system will be referred to as “pressure system”.
However, in a case of performing the purge processing in the pressure system, there has been a problem as will described below.
In the case of the suction-system purge processing, ink ejected from the head is sucked by the suction pump so that the ink can be discharged to the outside of the cap. Accordingly, waste ink in the cap can be eliminated comparatively easily.
However, in the case of the pressure-system purge processing, if the system is not provided with the suction pump for generating a negative pressure in the cap, there occurs a problem that the ink ejected from the head stays in the cap so that the ink cannot be discharged to the outside of the cap effectually.
As for this problem, it is not impossible to provide a suction pump even when the pressure-system purge processing is performed. Indeed, there is a solution that a suction pump is provided to eliminate the ink from the cap.
However, in such a solution, the suction pump is provided separately in addition to the pressure pump. Thus, there occurs another problem that the number of pumps increases, thereby causing disadvantages in terms of both the cost and the number of man-hours in comparison with the suction system in which ink suction and negative pressure generation in the cap can be performed with a single pump.
In addition, the inventor has examined a structure in which a cap has a large displacement between a time when the cap is in close contact with the head and a time when the cap is at a distance from the head. In this case, when the suction pump is fixed to a main body side as in the inkjet printer according to JP-A-2002-301831, it is necessary to provide a counter measure such as a sufficiently long flexible tube for connecting the cap having the large displacement and the suction pump having no displacement.
However, the longer such a flexible tube is, the lower the suction capability of the pump is. It is therefore necessary to provide a pump having higher performance, causing increase in size or cost of the pump. In addition, as the flexible tube is longer, the risk that the flexible tube moving following the cap is caught or entangled by something becomes higher. Further, when a barrier-free space for allowing the flexible tube to move smoothly is secured to prevent the flexible tube from being caught or entangled by something, the size of the printer may be increased correspondingly to the secured barrier-free space.
When, for example, a structure is adopted in which a suction pump moves retaining the position relationship with a cap, such an excessively long flexible tube is dispensed with. Accordingly, these problems may be solved.
However, for such a countermeasure, it is also necessary to secure a space for allowing the pump to move, still causing increase in the size of the printer. In addition, the movement of the pump may provoke a failure of the pump.